Enzymes are used to process a variety of agricultural products such as wood, fruits and vegetables, starches, juices, and the like. Typically, processing enzymes are produced and recovered on an industrial scale from various sources, such as microbial fermentation (Bacillus α-amylase), or isolation from plants (coffee β-galactosidase or papain from plant parts). Enzyme preparations are used in different processing applications by mixing the enzyme and the substrate under the appropriate conditions of moisture, temperature, time, and mechanical mixing such that the enzymatic reaction is achieved in a commercially viable manner. One area where enzymes play an important role is in the area of corn milling.
Today corn is milled to obtain cornstarch and other corn-milling co-products such as corn gluten feed, corn gluten meal, and corn oil. The starch obtained from the process is often further processed into other products such as derivatized starches and sugars, or fermented to make a variety of products including alcohols or lactic acid.
The process of starch recovery from corn grain is well known and involves a wet-milling process. Corn wet-milling involves many time consuming and costly steps, which include steeping the corn kernel, grinding the corn kernel and separating the components of the kernel. Dry-mill processes of making fermentable sugars (and then ethanol, for example) from cornstarch facilitate efficient contacting of exogenous enzymes with starch. These processes are less capital intensive than wet-milling but significant cost advantages are still desirable, as often the co-products derived from these processes are not as valuable as those derived from wet-milling.
Thus, for dry milling, there is a need for a method that improves the efficiency of the process and/or increases the value of the co-products. For wet milling, there is a need for a method of processing starch that does not require the equipment necessary for prolonged steeping, grinding, milling, and/or separating the components of the kernel. For example, there is a need to modify or eliminate the steeping step in wet milling as this would reduce the amount of waste water requiring disposal, thereby saving energy and time, and increasing mill capacity (kernels would spend less time in steep tanks). There is also a need to eliminate or improve the process of separating the starch-containing endosperm from the embryo.
The present invention relates to a self-processing transgenic corn (Zea mays) plant that has incorporated into its genome a synthetic α-amylase gene (amy797E), encoding a thermostable Amy797E α-amylase capable of processing starch in plants. Upon expression and activation of the α-amylase, the plant or plant part processes the substrate upon which the α-amylase acts. This “self-processing” results in significant improvement in making starch available for fermentation. Thus, methods which employ such plants and plant parts can eliminate the need to mill or otherwise physically disrupt the integrity of plant parts prior to recovery of starch-derived products. The transgenic corn event also has incorporated in its genome a manA gene, hereinafter called the pmi gene, encoding a phosphomannose isomerase enzyme (PMI), useful as a selectable marker, which allows the plant to utilize mannose as a carbon source.
The expression of foreign genes in plants can to be influenced by their location in the plant genome, perhaps due to chromatin structure or the proximity of transcriptional regulatory elements close to the integration site (Weising et al., 1988, Ann. Rev. Genet. 22:421-477). For this reason, it is often necessary to screen a large number of events in order to identify an event characterized by optimal expression of an introduced gene of interest. For example, it has been observed in plants and in other organisms that there may be wide variations in levels of expression of a heterologous gene introduced into the chromosome of a plant's genome among individually selected events. There may also be differences in spatial or temporal patterns of expression, for example, differences in the relative expression of a transgene in various plant tissues, that may not correspond to the patterns expected from transcriptional regulatory elements present in the introduced gene construct. Therefore, it is common to produce hundreds of different events and screen those events for a single event that has desired transgene expression levels and patterns for commercial purposes. An event that has desired levels or patterns of transgene expression is useful for introgressing the transgene into other genetic backgrounds by sexual outcrossing using conventional breeding methods. Progeny of such crosses maintain the transgene expression characteristics of the original transformant. This strategy is used to ensure reliable gene expression in a number of varieties that are well adapted to local growing conditions.
It would be advantageous to be able to detect the presence of a particular event in order to determine whether progeny of a sexual cross contain a transgene of interest. In addition, a method for detecting a particular event would be helpful for complying with regulations requiring the pre-market approval and labeling of foods derived from recombinant crop plants, for example, or for use in environmental monitoring, monitoring traits in crops in the field, or monitoring products derived from a crop harvest, as well as for use in ensuring compliance of parties subject to regulatory or contractual terms.
It is possible to detect the presence of a transgene by any well-known nucleic acid detection method including but not limited to thermal amplification (polymerase chain reaction (PCR)) using polynucleotide primers or DNA hybridization using nucleic acid probes. Typically, for the sake of simplicity and uniformity of reagents and methodologies for use in detecting a particular DNA construct that has been used for transforming various plant varieties, these detection methods generally focus on frequently used genetic elements, such as promoters, terminators, marker genes, and the like, because for many DNA constructs, the coding sequence region is interchangeable. As a result, such methods may not be useful for discriminating between constructs that differ only with reference to the coding sequence. In addition, such methods may not be useful for discriminating between different events, particularly those produced using the same or similar DNA construct unless the sequence of the flanking DNA adjacent to the inserted heterologous DNA is known.